Weekdays should be fine. Weekends could be tougher depending on location. We weren't able to camp this weekend because as of Wednesday I couldn't find a reservable spot within 200 miles. Summer weekends in the PNW. Only first come first serve and with a Friday afternoon arrival I got nervous. Not saying you wouldn't find something, but it could be work. Course with a TC it's pretty easy to just pull over on some FS logging road. But that doesn't work for our size TT.
Also if you don't have cell service, you can't make a reservation. We ended up in a WM this summer after calling a cg to make a reservation and leaving a VM. We lost service after that so never got their call to call back and confirm one of their last spots. By the time we showed up they were full.