I put tie-downs in my driveway to guy down my boat canopy during the summer. I dug 2 foot holes, crisscrossed rebar diagonally into the ground, poured concrete, and sunk heavy duty eye-bolts with alternating nuts and washers into the concrete. I will be doing something similar this summer with posts, sinking them into concrete, with rebar through them.
This is actually quite simple.
Step one - use PVC electrical conduit, not PVC pipe.
Step two - provide an access point (such as an LB, or a junction box) for every 360 degrees (at most) of turn. This will be something that remains accessible by removing a panel when the walls are closed back up, like any other junction box access.
If you have 6 90 degree turns, either put in 3 90's and an access point (if using an LB, that can be the access point) or 4 90's an an access point, depending how the run works out best for placing the access point. Use electrical conduit sweeps, not plumbing 90's or 45's.
3, access point, 3 would be most balanced, but
4, access point, 2 is also fine.
There's no need to get too excited about leaving a pull string in place - you can always vacuum one in, or pull one in while pulling an old cable out. Do it, or don't do it, as you prefer. Do make sure that the ends of your conduit terminate in junction boxes from which the cables leave by fairly tight holes or grooves (or through proper cable clamps, but that can be tricky with pre-terminated cables), so that your conduit does not become your new rodent pathway and nest.
Best Answer
A lot of structural steel and piping comes galvanized already. For instance most silver/gray colored iron pipe. (not black pipe used for gas; apparently methane or its additives don't play well with zinc.) And you can get galvanized pipe fittings to link them, in most shapes.
Piping may not be the way to go. You may want to go with sectional steel channel, one being the Unistrut style and its many clones. Again, available galvanized.
If you really wanted to go PVC or EMT conduit, despite the weight load, consider designing a truss. Crazy large geodesic domes are made using EMT conduit as the structural members.
There are many ways to arrest corrosion other than galvanizing. My preferred way is to knock off the rust with a wirebrush or sander, then Rustoleum 7769 Rusty Metal Primer which seems to control light surface rust reasonably well, then any of a variety of topcoats (primer alone will not hold; look any any automobile that's driving around with rust busting through the primer).