Uhhh what? At least 1 baffle to set up a return chamber: you'll see evaporation more readily in a smaller chamber since it will be the only one without a set water level.
I would cut it equally to 4 sections lengthwise - first for the drain inlet and socks, slight drop in to the second for the fuge, third for the skimmer (outflowing baffle set to whatever target height your skimmer needs), and the fourth is your return pump chamber.
Otherwise, there are LOTS of photos of sumps available on a general search with your desired equipment. I don't see the need for ceramics, I'd personally opt for a bunch of live rock with some macro growing on it.
Even in a large sump evaporation is easily noticed in my experiences, and I'd add, working with a larger volume of water in a sump without baffles, ATOs, which will fail sooner or later, may not be necessary.
For that matter, sumps aren't strictly needed either.
As macro algae are implicated in the demise of corals through their increased release of labile DOC a much better choice for an unlit sump would be some ocean sourced base rock with cryptic sponges.
Here's a data bomb if you're interested in reading up on the science.
Indirect effects of algae on coral: algae‐mediated, microbe‐induced coral mortality
https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1461-0248.2006.00937.x
Influence of coral and algal exudates on microbially mediated reef metabolism.
Coral DOC improves oxygen (autotrophy), algae DOC reduces oxygen (heterotrophy).
https://peerj.com/articles/108/?utm_source=TrendMD&utm_campaign=PeerJ_TrendMD_0&utm_medium=TrendMD
Role of elevated organic carbon levels and microbial activity in coral mortality
http://www.int-res.com/articles/meps2006/314/m314p119.pdf
Effects of Coral Reef Benthic Primary Producers on Dissolved Organic Carbon and Microbial Activity
Algae releases significantly more DOC into the water than coral.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0027973
Pathologies and mortality rates caused by organic carbon and nutrient stressors in three Caribbean coral species.
DOC caused coral death but not high nitrates, phosphates or ammonium.
http://www.int-res.com/articles/meps2005/294/m294p173.pdf
Visualization of oxygen distribution patterns caused by coral and algae
https://peerj.com/articles/106/
Biological oxygen demand optode analysis of coral reef-associated microbial communities exposed to algal exudates
Exposure to exudates derived from turf algae stimulated higher oxygen drawdown by the coral-associated bacteria.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3719127/
Microbial ecology: Algae feed a shift on coral reefs
https://www.nature.com/articles/nmicrobiol201661
Coral and macroalgal exudates vary in neutral sugar composition and differentially enrich reef bacterioplankton lineages.
https://www.ncbi.nlm.nih.gov/pubmed/23303369
Sugar enrichment (DOC, carbon dosing) provides evidence for a role of nitrogen fixation in coral bleaching
https://onlinelibrary.wiley.com/doi/full/10.1111/gcb.13695
Elevated ammonium delays the impairment of the coral-dinoflagellate symbiosis during labile carbon pollution
https://www.sciencedirect.com/science/article/pii/S0166445X19307192
Excess labile carbon promotes the expression of virulence factors in coral reef bacterioplankton
https://www.nature.com/articles/ismej2017142
Unseen players shape benthic competition on coral reefs.
https://www.ncbi.nlm.nih.gov/pubmed/22944243
Allelochemicals Produced by Brown Macroalgae of the Lobophora Genus Are Active against Coral Larvae and Associated Bacteria, Supporting Pathogenic Shifts to Vibrio Dominance.
https://www.ncbi.nlm.nih.gov/pubmed/27795310
Macroalgae decrease growth and alter microbial community structure of the reef-building coral, Porites astreoides.
https://www.ncbi.nlm.nih.gov/pubmed/22957055
Macroalgal extracts induce bacterial assemblage shifts and sublethal tissue stress in Caribbean corals.
https://www.ncbi.nlm.nih.gov/pubmed/23028648
Biophysical and physiological processes causing oxygen loss from coral reefs.
https://elifesciences.org/articles/49114.pdf
Global microbialization of coral reefs
https://www.nature.com/articles/nmicrobiol201642
Element cycling on tropical coral reefs.
This is Jasper de Geoij's ground breaking research on reef sponge finding some species process labile DOC 1000X faster than bacterioplankton. (The introduction is in Dutch but the content is in English.)
https://www.rug.nl/research/portal/files/14555035/13completethesis.pdf
Sponge symbionts and the marine P cycle
https://www.pnas.org/content/112/14/4191
Phosphorus sequestration in the form of polyphosphate by microbial symbionts in marine sponges
https://www.pnas.org/content/112/14/4381
Differential recycling of coral and algal dissolved organic matter via the sponge loop.
Sponges treat DOC from algae differently than DOC from corals
https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2435.12758
A Vicious Circle? Altered Carbon and Nutrient Cycling May Explain the Low Resilience of Caribbean Coral Reefs
https://academic.oup.com/bioscience/article/66/6/470/2754308
Surviving in a Marine Desert The Sponge Loop Retains Resources Within Coral Reefs
Dissolved organic carbon and nitrogen are quickly processed by sponges and released back into the reef food web in hours as carbon and nitrogen rich detritus.
https://www.researchgate.net/publication/279061640_2013_deGoeij_Science_Sponge_loop
Natural Diet of Coral-Excavating Sponges Consists Mainly of Dissolved Organic Carbon (DOC)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3934968/
The Role of Marine Sponges in Carbon and Nitrogen Cycles of COral Reefs and Nearshore Environments.
https://search.proquest.com/openvie...9d1e5/1?pq-origsite=gscholar&cbl=18750&diss=y
Microbially mediated nutrient cycles in marine sponges
https://academic.oup.com/femsec/article/95/11/fiz155/5582607
