Been a few years but 99 is stop and go as you go through every town it passes through, 5 is non stop, unless there's accidents. You live in CA so you must know that. My go to for finding places to stay www.campgroundreviews.com/
I would take I-5 just to avoid all the on-off traffic at the various cities. Both roads are rough. Do what Edd505 recommended- check out www.Campgoundreviews, as camp grounds can change from year to year and it's been a long while since I have stayed in the central valley.
2018 Durango 318RLT Ford Lariat F250 Former RVIA master tech.
I can say that the stretch of 99 between B'field and Fowler's not bad if you can miss traffic. We've got a farm just outside Ducor, off 65, and that's the way we normally go to Porterville, where our manager's office is, but occasionally we'll do a through on 99 to Fowler, where our packing house is. Grapevine was pretty bad on the L.A. side last year, especially towing an empty 30' triple-axle GN, but wasn't bad once we got up "on top". 210 sucked, too. Coming back, with a small tractor on the trailer, it was better with some weight on. Personally, I've not been N of B'field on 5 in years, so can't speak to that. 58's not too bad on the divided road, but the 2-lane is a bit rough, and traffic can be heavy. Never been E of Kramer Jct, as we normally cut down 395. Now, THAT stretch of road =really= sucks, both for condition and for the truck traffic.
2002 GMC Sierra 2500 HD Duramax Crew Cab 4x4 * Banks Monster Exhaust * B&W Turnover Ball with 5th Wheel Companion * 2017 KZ Durango 1500 D277RLT Fifth Wheel * 1936 John Deere Model A * 61 Year International Flying Farmer Member