I thought I had mastered the "threaded fastener" back in my pre-teen years.
Certainly was able to swap gears and rebuild the transmission on my Formula Ford to adjust for each track and all sorts of road racing mechanical chores many years back as well.
Our coach has these on the "Dog house" engine cover and did have them on the entry steps over the house battery area.
I spent some 2+ hours removing the 4 on the steps, initially using the large i.e. widest blade screw drive ACE hardware had. The slot is very wide and long so this did not work very well. On the steps once broken loose with the large screw driver I used vice-grips to remove them. I replaced all 4 on the step entry way with similar coarse thread lag bolts with 9/16" heads.
I planned on removing the engine cover and add more sound proof insulation but can not get eh *&^%$ things out. There are 6 with 2 in the rear and 2 on each side. I do not want to remove these with brute force like I did on the steps. Lag bolts will not be flush here nor look very good.
What tool is used for these? Under the dash area not enough clearance to crawl under with the long and large screw driver in any case. As the slots are both longer and wider than the blade it slips.
The channel-lock pliers already scrapped the edges a bit before I abandoned the task and grabbed an IPA.
Any suggestions welcome.
Perhaps calling a mobile RV person and paying the big $ to have him/her remove the cover and add the insulation is an option. Assuming I can find one in the Yuma area we are heading to after Borrego Springs, CA.
These days it seems less expensive both time and $ wise to hire someone than buy specialty tools used only 1-2 times.