3 1/2" drain opening
I'd tow it the other way around, but it's a great, simple design.
Colt and ROV are promising
Might be overkill/expensive, and seems to assume using two struts for every door.
You can't get these anymore, at least not these dimensions.
The exterior port does not wire to a charge controller unless you add one!
Teardrop Fix-It-Shop reproduces exact replicas of Kit and Kenskill Teardrop Trailers and supplies aluminum extrusions and moldings. These trailers are available as a pre-cut do-it-yourself kits or can be built to order. Based in Victor, Montana.
Links to http://www.monkeytailportablesanitation.com/ which is in Florida?
The compact wind generator is interesting, but the rest is a bit odd.
Might be good background for designing grid-supplemental and EV extender storage.