After a month off from this I returned (at the Packrat Palooka boss fight) expecting to be able to head back into town to buy some upgrades.
Sadly no such luck, as the way is blocked, so I'm either faced with loading an earlier save (at least an hour lost) or persevering with the boss fight.
Had maybe 20 attempts over the last few days (the best one left him with a slither if health left), but no joy yet. I think my main issue is that because I haven't upgraded anything, I can't hold enough Boombat or Thudslug ammo, and everything takes too long to re-load.
I'll have another few goes, but maybe just give in an load up an earlier save