Hi! We just returned from a month and a half stay in our 5th wheel in the mountains of New Mexico and Colorado with our Rex and Rowdy. Our 5th wheel has floor vents and neither of our guys had any problems with them, even when they were little. Rowdy is 4 1/2 lbs now, and he was in the 5th wheel for 3 weeks last year when he was 4 months old. I didn't even think about it being a problem and it wasn't.
They both did great this year - Rowdy is almost a year and a half and Rex is 5 1/2 months old. The only problem this year is that they came down with diarrhea after about a month. They probably had giardia - but it doens't usually show up without lab work. We took them to the vet in New Mexico and they decided to treat them for giardia and they did great, once we started the antibiotic. It was not fun to have 2 little guys with runny poop!!!
Thankfully, they didnt' seem to feel sick or stop eating! They were their usual selves, just with runny poop!!!
Other than that, they did great on the trip. We bought 2 of the metal X pens and put them together so that we could set it up outside the trailer and then they could get into it off leash and romp and play in the grass. They loved it!!!
Good luck with your travels - we love traveling with our guys - they are great conversation starters and you'd be surprised at how many Yorkies there are in RV parks - it's amazing, I think they are the most common breed that we see.