the cracks in the paint are either because of the use (or overuse) of filler or due to rusting underneath.
for the trunk, you need to get everything out, all the cloth and cng cylinder, wash out all the dirt with water. dry it well, then clean the rust and spray rust treatment. i would do some white paint over the patches and keep an eye on it for a few months, if the rust doesn't come back, then you are good, get a painter to match only those patches.
the rust treatment part must be done by the owner, don't expect good work from local painter. they don't have that kind of time