Steve
I have to drive US 199 east and west bound to get to Grants Pass at least 4-5 times each year, since that is my best way to get to the I-5 corridor reliably and in about 2 hrs one way. I'm driving a 36' Beaver, which is almost 38', plus a SUV in tow.
As Roy pointed out, US 197 is a short cut from US 199 by Hourichi to US 101 north of Cresent City. That short cut gets you out of taking US 199 through the Redwoods National/State park since there are several tight turns for a long rig.
I may have to disagree with Roy on the rest of US 199 to GP. I feel that there are really only 2 bad spots to watch and that I slow down greatly for at mile marker 26.5 and between 22-23 These 2 spots are minimum narrow road, no shoulder and at MM 26.5; outside curve lane guardrail installed right on the white road side line, with cliff drop off down into the Smith Rover below, inside curve lane has a sheer rock wall on the with minimal shoulder, and there is also a preceding very quick S-curve then a 120deg blind curve. I just go very, very slow (10-15MPH) at that spot since you cannot immediately see what is the oncoming traffic till almost too late while in the turn.
US199 is used as the primary route for loaded logging tractor-trailers going to/from the local sawmills, or fully loaded cut lumber trailers coming from the mill e.g.: South Coast Lumber in Brookings, OR, as well for all of the trash hauler rigs from the coast going to the Medford area land fill, so they run US199 full bore all the time and they are much longer than 42' Beaver with a tow. US199 in CA has lots of slow vehicle pull outs for other to safety pass You'll also see the assortment of single 45'-53' standard and double short trailers by Rediway, UPS, FedEx and other rigs.
Unless you are willing to go 150+miles out of your way for a just marginally better route (my opinion) for a I-5 Grants Pass to southern OR coast destination like Brookings/Gold Beach or far northern CA destination like Creasent City, US 199 is your best bet.
The rest of US199 is curvy and rolling, but a pleasant enough drive to handle. You will climb and decent 2 passes going over the Cosatal range, but they are only 1500' or so. For us on the southern OR coast, US199 is just a fact of life. Note: limited/no cell coverage in several stretches of the CA canyons of US 199 for many miles.