Why would the conduit have to be above ground? Seems to me you could put it on the downstream side, and bury it just above the culvert. You probably have a foot of dirt on top of the culvert anyway, so it should be easy to cover it up.
What I have on top of the culvert is about 3' of pit run rock, which, in these parts, is rock in chunks from bowling ball size down to maybe hen's egg size. Clearly crushed and very angular.
The entire roadbed is built up above natural grade. The stuff has an angle of repose of about 45-50 degrees. (Vertical is 90 degrees). Any trench is going to be more of a shallow V shape than the usual square-cornered trench, and the pit run is not suitable for backfilling.
The roadbed has been compacted with a vibratory roller. If I dig a trench in it, the trench wiil be at least 6' wide for a 3' depth, and I am going to have to re-compact whatever I backfill. I don't have a roller, and renting one would be a lot more expensive than puting the trench below natural grade.
Same for the transformer idea. Around here the power company charges ~$3000 each, I know since I have two already. And, I still would have to dig the trench & lay the line to the transformer. In Southern Oregon, that is the customer's job. All the power company does is inspect before they will energize your lines.
I already have a separate transformer feeding the wellhouse, with 200 Amp service. I now need to put about 75-100 feet of line from the wellhouse to the RV pad.