Ratchet & Clank: Going Commando

The best place to level up weapons is planet Damosel. My strategy was a little bit different than yours, but here is what I suggest:

1) When you land on Damosel, smash up all the breakable around the ship. Load up on Synthenoids and shields at the MegaCorp vendor, because they won't appear in ammo boxes. You'll see a bunch of protopets wreaking havoc on the street. Put on your shield and charge out there, Sheepinating everything that gets in your way (though you may have to lay off the Sheepinator and just let them bounce off your shield for a while, if that isn't levelling up fast enough). Use your plasma coil on the exterminator bots that show up at the end of the road. Once their gone, keep Sheepinating the protopets and smashing up the street for bolts. When you're bored, destroy the mailbox and move up the ladder.

2) At the top of the ladder are four more exterminator bots. Plasma Coil those and move on. Jump down to the lower platform, where you will find four mailboxes and a throng of protopets. Three exterminator bots will land after you. Plasma Coil them, then when they're gone, bring out your Synthenoids. Just keep bouncing around with your Shield Charger on and let the Synthenoids take out all the protopets. When your Synthenoids run out, take out your Sheepinator and toast the remaining critters.

3) When they're gone, you can move through a large door into an interior area. This is more of the same: Sheepinate protopets and Plasma Coil exterminator bots. When they're all dead, you move through another door back onto the street. Now you'll find stronger exterminator bots launching acid grenades at you. Discharge any remaining Plasma Coil or Shield Charger ammo you have, and then just die. (It's important not to go past this area, because once you hit the continue point, you won't have as many enemies regenerating.)

4) After you die, you should respawn back at the ship. Head toward the street, but then turn left and activate the Giant Clank platform. Blast off to the moon. As soon as you get there, exit out of the battle and return to Damosel. Now all the boxes will have returned.

Now, repeat steps 1-4 until your weapons have levelled up. Be warned, this will take patience, especially on the part of the Synthenoids. I had to do it many, many times, but when all was said and done, I ended up netting 400,000 bolts from the exercise.

Addtional strategies: You can level up the Sheepinator with the squirrels on Todano or the little anklebiters on Smolg It just won't go near as quickly as on Damosel. And Boldan is very effective for levelling up the Plasma Coil. And the for the Lava Gun, you can level that up pretty much anywhere. I did it on a combination of Tabora and Dobbo. But my simple advice is: don't. Don't level up your Lava Gun. Bring it out when you need its wide range and then put it back again, because the Meteor Gun is in every way inferior.