Motorhomes have fixed-mount tanks and fall under different rules in the US. For starters, there is no recertification period. They're permanent.
Which is not to say that they can't deteriorate. Responsible licensed fillers will be able to observe that a tank is in good shape (no deep result, cracked mounts, dents, etc.). And if it is in bad shape, she or he is encouraged not to fiddle with it.
For the most part, though, you should be able to see damage by yourself. And if it is in sorry shape, don't try to sneak it by. Get it replaced at a full-service propane company.
So, then, the filling process is easy. You take it to a propane filling outfit and have the person fill it. You'll need to have all propane appliances turned off; all humans must leave the moho; and the wheels must be chocked. The filler will use the bleed valve to determine the full point (i.e., fill by volume), there being no reasonable way to fill by weight instead.