conduit to connect panels outside
Honestly, I would affix a chunk of marine plywood to the pole, prime it, paint it with exterior paint, and attach the RV panel to that.  That will give you more freedom to position it for a &quot;back to back&quot;, &quot;out the bottom of the RV panel and then in the back of the main&quot; with a single bevel 90, or down, over and up with two 90s.
Given the very short distance, the cost of wire is negligible, so I would use #3 copper.  I'm not a huge fan of copper for feeder, but it's the most compact, so it'll fit in the smallest conduit.

Here's the thing about those &quot;50/30/20&quot; RV stands.  Generally, you're expected to install one of those per RV site.  And then, the RV is expected to use the one socket that is compatible with its power.
You keep talking like using all three of them at the same time, you're not required to provision for that.  You only need to provision for the largest socket available to any given site, and you ignore all the smaller sockets.
If you follow the &quot;One 50/30/20 panel per site&quot;, then it's pretty simple.  You calculate based on 50A/12,000 watts per panel/site, and then apply the favorable derate that Ed Beal mentioned from 551.73.

90% if 2 sites (so 90A for two 50/30/20 RV stands)
80% if 3 sites (so 120A for three 50/30/20 RV stands)
75% for 4 sites
65% for 5 sites
60% for 6 sites
55% for 7-9 sites (thus you can support seven 50A sites from 200A service)

So again, you don't have to provision more sockets than you have RV sites.  You just count your RV sites and provision that many sockets, largest first.
And follow what Ed Beal says about how 50A RVs take a lot more power than 30A RVs.  That is  because 50A RVs take 240V power, not 120V.  They take over triple the power of a 30A.

50A/240V sockets are 12,000 watts
30A/120V sockets are 3,600 watts
20A/120V sockets are 2,400 watts
By the way, tent sites follow a special rule and you must only figure them for 600 watts.

And then apply the derate as Ed says.
Like I say, given your 100A provisioning, I would just go ahead and install two 50/30/20 RV subpanels at wherever you expect will be most useful.   Because the subpanels are good for 100A busing, you don't actually need to give them separate breakers - you can simply daisy chain from one subpanel to the next.  But the wire needs to be 100A.
Does it matter how many sites you support with two 50/30/20 RV stands?  Actually it doesn't -- no combination will exceed 100A.

2 sites: 12,000 x 2 = 24,000 W x 90% derate = 90A
3 sites: 12,000 x 2 + 3600 = 27,600 W x 80% derate = 92A
4 sites: 12,000 x 2 + 3600 x 2 = 31,200 W x 75% derate = 97.5A
5 sites: 12,000 x 2 + 3600 x 2 + 2400 = 33,600W x 65% derate = 91A
6 sites: 12,000 x 2 + 3600 x 2 + 2400 x 2 = 36,000 W x 60% derate = 90A