I recently installed the light set up- no splicing, roadmaster base plates, demco duo braking system in a 2018 wrangler JL.
After watching several how to vids i watched i went with the engine compartment, next to the battery. Out of 4-5 vids i watched only 1 had it installed on interior of vehichle.
Only issue i could see would be the length of vacuum hose needed, not to sure about that, but demco tech are quite helpful.
2021 Alante 27A