My wife's older Trek hybrid, steel-framed 730, has 2 drain holes on the seat stays, near the rear dropouts. This bike has been on the back of our RV, on a bike rack, for 3000+ miles, being used at various times on this trip. When I took the bike off the last time, moving it on the back wheel with the front wheel up, two streams of water shot out of the drain holes; a lot of water drained out. I've noticed some rusty water in the past, but this was extreme (although this water wasn't rusty).
Should I be concerned? Is there something I should do? Should the bike be considered "suspect" in terms of the frame (I don't know how long this has been going on).

Opinions please. Thanks.

Don't go screaming downhill based on my advice, but in my experience, rust doesn't attack as fast or hard as a lot of us think. All my bikes but one are steel, and two lived near the beach for years (one's a mid-'80s Trek tourer). My old Bridgestone mountain bike has been completely submerged in fresh water many times, and another steel MB sat out in salt air for two years when I lived on the coast. My Atlantis and Rambouillet get better care and have been Frame Savr'd, but I ride them in rain etc. without any special treatment.
None has more than superficial rust that I'm aware of, though I do worry about the fork on the Trek sometimes. It's my all-purpose, all-weather bike, with tens of thousands of miles on it (guy I bought it from rode from Indiana to Nevada on it, and I've had it almost 20 years). The other day I was bumping along over some rough pavement when it occurred to me that it's older than my kids.

Park the bike in the sun for a few hours to dry things out. Squirt some WD-40 into the vent holes. Don't worry -- it takes decades of neglect for a steel frame to rust to the point of failure.

I wouldn't recommend WD40 unless you wanna squirt it in there all the time, because as soon as it disappears, rusting comes back stronger. WD40 is an extremely strong solvent.

Actually I wouldn't worry about it at all as long as you keep riding your bike, because regular vibrations usually shake the rust off on the inside because it isn't exposed external elements as much.

I have that same bike (my commuter) and it's been through several winters of the most salty, sandy, gunky crap imaginable. It's not pretty (rust-wise) but it's also not a lightweight thin-tubed custom steel road bike either. I have one of those too.

Is it possible to mount it on the RV so rain does not accumulate inside?

If your really concerned which I don't think you need to be there's always https://www.treefortbikes.com/product...r-Aerosol.html

I`m sure you heard that stuff about WD40 somewhere but unfortunately none of it is true. There are more urban myths floating around the Internet about WD40 than any other consumer product I`m aware of.

The WD40 website has a complete FAQ plus a lengthy list of recommended uses. It might be worth a visit. Its original claim to fame (and the reason for its development in the first place) was based on its effectiveness as a rust inhibiter when sprayed on the outer skin of military missles. Its not a strong solvent and any properties it has as a degreaser are based on it consisting largely of light mineral oil - which basically dilutes heavier oils and greases with a little elbow grease.

However - that light mineral oil will displace water and permanently adhere to metal - since all metals are porous by nature. If you doubt that then an interesting challenge for you might be to try to paint any metal object that been treated with WD40. As per your post since its a strong solvent - the metal should have been perfectly prepared for painting. Good luck!