Jaffa,
'Nuthin's impossible
With a port-a-pot, you have to lift it up, take it to where ever you're dumping it, and do the unpleasant deed.
Then a quick rinse, and you're done.
With a permanant toilet, you have to tow the whole trailer to the dump station, get out the "sort of clean" drain hose, hook it up to your trailer, then slip it in the drain hole.
Then pull the knife valve to dump, then go inside to flush/rise the holding tank.
Then use a hose to rinse your drain hose, and put it away.
Meanwhile, your nose itches real bad...but it's okay to scratch it 'cause you were careful and didn't get anything on your hands...right?
If you use it a lot, and don't want to move the trailer just to dump, you can use a portable tank on wheels, but then you have to do everything twice.
Another advantage to the portable is when you're driving home, if you really have to go
and there aren't any restrooms in sight, you can just pull over and "relax".
If you're starting from scratch, installing a toilet isn't hard to do.
The trailer may need to be bigger than a standard tear, but that's okay because it has to suit you.
Rob
Waiting for "someday" will leave you on your deathbed wondering why you didn't just rearrange your priorities and enjoy the time you had, instead of waiting for a "better" time to come along...