There are lots of places that will rent you a travel trailer. There are less that will rent you a 5th wheel although the only place I found was in Arizona. I've never heard of a place renting both.
Anyways, this is the road we went. We rented a cheap travel trailer. It was poorly constructed(wires inside the cabinets for example), but everything worked and we had a great time. So we decided to buy based on our good experience. We got a mid grade 5th wheel thinking that would be better than the TT we rented.
Going from renting to buying has not been smooth. I'd rather have that cheap travel trailer than the money and time we've spent on this "mid-grade" 5th wheel.
The rental places have a full time staff to handle all the recall issues, leaks, maintenance, etc.. So you get a reliable unit for that week. Owning, you have to pay storage, registration fees, maintenance, repairs, deal with mice, etc...
There are some on this forum who claim different manufacturers are more reliable than others. That may be true, but I've discovered on these forums that our experience is not atypical...
Another option would be just to rent anytime you need an RV. Or be VERY patient and wait until you get a recommended unit used or new at a discount.
My 2 cents.