16's are very common. RVs and duallys still use 16's, and a lot of vehicles out there run 16's. I do not know about other countries.
Would it not be easier to change the trailer tires rather than the RV tires/wheels? Seems if you have 6 on van and 2 (or 4) on trailer that the trailer would have less to change.
If you are talking about a typical cutaway RV van chassis with disk up front and drum on the rear, then , no. The drums are fine, they have a lot of power as is. Keep in mind that big rigs use drums on the rear too, though they are air brakes with a lot more more to it.
Personally, if I were starting from scratch the 17 wheels might be attractive since I live over-sized tires anyway, but go to 19 and you have a lot more commercial tires available too.
Stick with the factory size tire and you will have no issues.
