I need to wire two RV outlets, one is 30 amp and the other is 50 amp. They will be about 100 feet apart but distance from 200 amp service to the last one will be 250 feet. What size subpanel should I install and size if wiring needed? Also does anyone manufacture and insulated underground cable sufficient for this application?

The cheaper way is to run 2/4 URD quadplex direct buried. That's good for like 95 amps but at 250' you will have voltage drop. The best way is to sleeve three #2 THHN (cu), and a #4 THHN in an 1 1/4 PVC pipe. That would normally be good for 100a but with voltage drop you'll get about 80 amps. Any electrical supply house should have everything you need.