Another link you may find helpful is this one:
Post #297 on the last page has a handy downloadable spreadsheet. It can be filtered by manufacturer, length, etc. and a little chart at the bottom will give you average axle
, tongue, and total weights. Cool!
Since you mentioned Casitas, know that 17' deluxe models can be pretty tongue heavy, which limits what you can pull them with. Don't know if that's an issue for you or not.
Good luck with your search.