Taking 36 from Manzanita would involve driving your rig through the Park on the main road 89. It is a narrow and curvy road. Doable, but you may not enjoy it. Use your toad to explore the Park and see it you want drive your A on that stretch.
While at Lassen, drive over to Butte Lake in the NE corner of the Park. The trail to the top of Cinder Cone is a bit of an effort, but the views from the top are incredible. You are looking down on a surreal and bizarre kaleidoscope of colors in the lava formations below you. Also visit the Subway Cave in Old Station.
The fastest way is 89/44 to Susanville, then 395 south.
89 through Quincy and Portola is a good road. Has curves, like any mountain road, but is plenty wide with shoulders and turnouts. If you go that way, you can visit the Lakes Basin by Greagle. Numerous lakes in a granite setting.