Flies to your ointment, wannabe boondocker. Love doing this ;)
Mex is right. Rent some cheap casita with water "nearby" and solar. See how it works for you in the off-season, i.e. spring and summer (I'm 90% positive that it won't work well).
Drive around and see other offgrid camps/casitas, talk to gringos that stay there all year round (there will be some, not too many). Check those camps in the evening when most of them are running generators. Yes, with +300W solar on the roof (with panels NOT shaded by trees etc) and when weather doesn't require A/C, many will run generators to watch TV - don't ask me why.
At some point you will realize that - unless you are a Mexican - you won't enjoy, and hardly will be able to live, in summer without A/C.
Then you'll start thinking generator, fuel, costs, break-downs (it does this). Portable "quiet" ones not meant for 24-hr use (not really quiet either, but this is what manufacturers call them). Stationary diesel monsters - easy on fuel, require a GOOD enclosure like cement blocks, if you want to be able to sleep and don't want turn you neighbors into your enemies.
Your generator always sounds less noisy to you than it does to your neighbor. I'm not kidding - even if age-related loss of hearing is at the same level for both you and the neighbor, you are placing it where it bothers you less. The neighbor is placing it where it bothers "him" less.
Then you'll start thinking on-grid camps - quiet, a lot more expensive than offrid ones, and where trailers are packed next to one another so that you can listen to evening news when your neighbor is watching his TV.
Some disclaimer - I'm a desert rat, like it dry, never been to Yucatan. Though it's not like Yucalandia is on the Mars and totally different from where I've been. Most likely the "off season" when it's too hot and humid to live without A/C lasts longer in Yucalandia.
20ft trailer for a long-term living - say, more than a month - is too small for 2 retirees. Works for some, not for majority. Think 23ft and longer, preferably with slides.
Half-ton truck - well, yes, it will pull TT up to 23-26ft, unless you are going to climb the mountains every day. Didn't have problems with my Chevy Suburban 1500 (same as F150 only with SUV vagon body). Though I added a separate transmission radiator (and didn't stray off paved or good gravel roads since it's a 2WD). Btw, really loved the "vagon" body - you should consider getting a canopy.
WD Hitch and anti-sway bar is a must, with trailer over 20ft.