Welcome! I am biased in favor of Fun Finders -- I have had two, a used one that lasted me seven years of hard usage and now a second one that has lasted nine years of even harder usage. Very solid, well built. Lots of off-pavement towing -- no leaks, no cracks, no damage. Amazing.
But honestly, I think Casitas are (on average) even more rugged -- they have that clamshell design. I think that Fun Finders may be a better value, dollar for dollar. They have more headroom than Casitas. The floorplans and bathrooms are better, I think.
But they are not made of two pieces of molded fiberglass.
2012 Fun Finder X-139 "Boondock Style" (axle-flipped and extra insulation)
2013 Toyota Tacoma Off-Road (semi-beefy tires and components)