50 amp RV outlet installation
Romex can't go outside

You would have to use cable rated for outdoor use, such as UF type.  

Alternately, while you are in conduit, you could simply use the correct single-conductor wire, i.e. the very common THWN-2.   

This is really pushing the limits of 3/4 conduit

3/4 conduit, supporting THWN single conductors, can support four 6 gauge conductors, fullstop.   No more room for anything else.  

Couple pieces of good news though.  You only need a 10 gauge ground, and it can and better be bare for space, and you can share the ground with the 20A circuit.   So you need three #6, two #12 and one #10 bare. Someone more code-geeky than I will have to tell you if that's legal in 3/4 conduit, but it's really pushing it.  

The trouble with "pushing it" with conduit is it makes the pulls really hard. It can either become a miserable afternoon, or force you to hire an electrician for the pull. And he won't touch it with a 10 foot stick of EMT unless everything you're doing is code perfect.  Because he has to sign off on all of it. 

Ease of pulling is a big deal for the DIY'er, and that is why I usually oversize my conduit by quite a bit. Conduit is cheap. 

Can't use wires without the cable sheath

They lose their physical protection, and they also lose their markings.  You can't use random unmarked wire.  It loses the weather resistance of UF.  You also can't pull shucked Romex or UF through a conduit, the insulation isn't tough enough to survive the trip. When you see THWN wire this will make sense. 

You would be unable to pull 6/3 UF through 3/4" conduit, let alone with another cable too! 

Wires through a hole in your house must be protected

There needs to be some sort of appropriate protection, like a conduit or cable which is rated for this use (and remember it needs to be outdoor cable too). 

If it were me...

I would use a short non-flexible conduit as a liner, with a junction box on both inside and outside.  The inside junction box would be a fairly large one, the outside could be a simple conduit body.  

At the inside junction box, I would transition from Romex (Indoor rated NM) to THWN-2 wires.  Outdoors I'd travel in ahem 1” or 1-1/2" rigid conduit, which looks pro and needs far fewer attachment points to the building. And since I have plenty of space, I'd give each circuit its own ground wire.  That would be me.