plastic welding is when you weld plastic!
seriously though this can be done but i'm not sure what plastics it works on, but motorbike repairs use it to fix fairing as its bloody expensive so if you put a crack in yours you can weld it up rather than buy a new panel.
i've only ever filled little things so i don't know what would be the best way to do this, but i assume if you use a small bit of fibreglass to patch the gap then skim over with filler,
sand back, fill, sand back etc til its nice and smooth
then plastic prime a few coats rubbing down to get it smooth. when you rub down the last few times use a very fine grade wet and dry with lots of soapy water to keep the paper clean.
then when your happy with the finish get the paint out! do it somewhere warm or the paint will go sh!tty, the primer can be helped along with a hot air gun.
take your time and you should be fine. the reason i say use fibreglass is because you want someting fairly strong as when you shut your boot, the force may crack filler alone so it would be a good idea to use something strong.
can anyone else offer any better suggestions of how to do this? bodywork is not a speciality of mine......
