Just so you have an idea of costs....
I'm installing 3 additional outlets in my motor home...
2 120volt 30 amp RV type (These are pigtail type outlets, 9 bucks each)
1 240 volt 4 wire twist lock 30 amp connector
Box, wire, clamps, wire nuts and 2 double breakers (30/15) 12 feet of 10-4 stranded wire
Total, not counting labor (I will do it myself, fully qualified) is about 100 bucks so far
Heavy guage wire (10 ga for 30 amps) is pricey, however it's worth it.
12 ga (20 amps) is much less expensive... but use a 20 amp breaker
Normal use, one of the 30 amp outlets will feed a special cord I made up for my old trailer, this originally was the power system for the old trailer, now it will be the power system for the picnic table,,, I mean, I just did nto wish to scrap the cord and outlets
Emergency use... If I don't need AC (IE: Cool night, just need furnance) in a blackout situtation I can power at least two other campers (30 amp each, though in truth 30 amp per leg is all the generator does) IF I can get by on one AC, then one other camper (The outlets will be labelet as to which one is which AC
Emergency use at home...... House has a 30 amp 240 volt inlet matching the outlet i"m putting in the MH