I am going to have to defer to the experienced wheelers since my only experience is from growing up driving on washboard roads.
I have been following this useful Forum to learn what the H3 is capable of.
You could check how much error is induced by putting the gage at different angles and see what the difference is between having the gage face verticle and at an angle at which you are planning to mount it. It looks like the gage has a ball for the indication so it won't suffer from friction.
I don't know when one gets to the stupid point but the door handle dragging may be it. If nothing is dragging, I can't see a problem.
Best regards, Happy Jack