I worked on cars and light commercials for years doing MoT repairs and welding. Handbrakes are a bloody nuisance. Often poorly designed and usually difficult to maintain, they have been the cause of more grief than almost any other part of the car. Here is the method I eventually arrived at.
Slacken the cable off a little and then take the drum off one back wheel, there is normally a large countersunk screw holding it on. If there is a pronounced lip inside the drum this can be the first problem area, sometimes needing two very big screwdrivers, or even small tyre levers, and the application of some vigorous hammering. Sometimes the shoes will come off too, no problem. Once the drum is off, use a small angle grinder to remove the lip. If the lip is really pronounced, think about new drums. Take off the shoes if necessary; this can be the second problem area as the springs can be very strong, I used to use a big screwdriver with a slot cut down into the blade, remove the auto adjuster and give it a good clean up with a wire brush and then use a little grease to lubricate it and make sure it moves freely. Clean up the backplate and the shoes and check that the friction material on the shoes is okay for thickness. Reassemble it all and then slide the drum on. Slide the drum off again and manually adjust the auto adjuster, then slide the drum back on. Do this a few times till the brake shoes begin to make contact when sliding the drum back on. Fasten the drum back in place. Take up the slack in the h/brake cable with the adjuster, and then pull the h/brake on and release it a few times.Pull it on HARD! This will centralise the shoes, and you will find that you can take the drum off again and take up a little more adjustment on the auto(?)adjuster. Do this a couple of times to take out all the slack between the shoes and the drum. After pulling the h/brake on and off a couple of times turn the drum to make sure it is still free before doing the adjustment. A little bit of contact will not hurt, the drums will probably be slightly oval anyway. Put the wheel back on and do the other side. Finally adjust the cable so that the brake begins to bite as soon as it is pulled up. It is a lot of messing about, and will probably need doing again next year, they get hot and dusty and have quite a hard life - most campers start off with a base vehicle that is much lighter than the finished article! Incidentally, when applying the handbrake, you should push the button in when you pull the brake on and release it to hold it on. Letting it click up the ratchet quadrant will wear it out eventually!! Have fun!!
.... i fank you