Two tools that are an absolute must for any remote soldering job would be portable versions of a soldering iron and heat gun. I have tried many different types in the past, but as of late, I just use these.
For basic heat shrink work, this
little torch does the job. It uses a cigarette lighter for fuel. The striking wheel and spring on the lighter must be removed to enable the heat gun to use it. I’ve found that a fresh lighter works better. Half full or less lighters tend to make you have to lay the tip very close to the shrink and at times, it can be burnt.
This torch will “not” do environmental splice sleeves. It does not generate anywhere close to the amount of heat needed. I have found out (the hard way) that it will actually burn through the sleeve before the sealant even comes close to flowing.
For environmental splices, you’re basically forced to use an electric gun with a curbed tip attachment.