afternoon, something you might want check before you buy a bunch of stuff is the size of breakers in your 5er. i know Montana uses one twenty amp and one thirty amp breaker, therefore when i installed a shore power box, i ran a single 50 amp circuit and split it at the box, that is neutral to neutral, single hot to each hot , and ground to ground ... in this way i only needed one fifty amp breakers and 6 guage - two wire, plus a ground in accordance with NEC code Article 551 - Recreational Vehicles and Parks - VII. 551.71 thru 552.60.
Or if you have say two thirth amp circuits in the 5er and you want to run smaller wire, you could run two thirty amp breakers in your main panel and run 8 guage - three wire, plus a ground to your shore power box. Your may also need to check local code to see if the variance is permitted.
I realize that you only need 10 guage ... but RV systems would tend to overload a 10 guage neutral, therefore 8 is recommended because the loads are ussually not balanced per circuit. If loads were balanced, then 10/3 would be ok up to 100 feet.