I agree with "myredracer", what advantage are you gaining/looking for? You don't describe what type of RV you have, but allude to a trailer with a single A/C unit. You're talking about going from 30 amps to 100 amps. What do you have that needs 100amps.
You also talk about a washer and dryer. If your intent is to power all the original equipment in the trailer (original 30 amp panel) from a new 50 amp box and then run new power (from the 50 amp box) to the washer dryer, you're doing a LOT of work and spending a lot of money for no real advantage. You're talking about spending at least $500-$1000 and a lot of labor to wash/dry clothes, when you could just do that in the evening.
If you're RV was one of those that had a lot of equipment like two A/C's, washer/dryer, fireplace and other power hogs, but was only built with a 30 amp service, it might be worth while to change to 50 amp.
Just so you know, on the 50 amp coaches, again 50 amp coaches have two legs of 50 amps each, the manufacturer divides the loads between the two legs. One A/C on one leg and one on the other, etc.