[JRTJH]

Parking on concrete reduces rolling resistance, so preventing the trailer from rolling with a gust of wind is probably more essential when parked on concrete than when parked on gravel. It sounds like you're not going to be in the local area while the trailer is parked, so you won't be available to "intervene" if any bad weather should blow in. I'd want my trailer as secure as I could make it in that kind of situation. In other words, large wheel chocks, tongue jack down and in good contact, slides in (so no twisting of the frame would happen if the trailer did move) and no power to the trailer, in case there were thunderstorms in the area, etc. In other words, winterized, parked and secured in place and prepared for bad weather.

I wouldn't put a lot of faith in XChocks for the "long haul" if you're not going to be around to check on them.... They are completely dependent on the tires maintaining pressure for their stabilizing forces to work. A small air leak in a tire would leave you with no chocking at all and, if you're in FL with your trailer in MN, well you get the idea. That's not the situation you'd prefer if a big wind were to blow in......

As for the slides, I've been told (can't provide a reference) that most slides will support "around 1000 pounds of static weight". I'd suppose that would change if the slide were being moved in or out, if the trailer was not level or if some other "out of the ordinary" were input into the situation. A couple of "heavy" (within reason, not fat lady from a side show weight) visitors shouldn't be a problem. I'd be more concerned that the sofa would support them than if the slide floor would fail..... YMMV