If you design your own map, it appears in a folder in ~\Documents\My Games\GratuitousTankBattles\scenarios
(note that Documents may be “My Documents” on various versions of Windows).
As there’s no way to share maps in-game yet, attached to this post is a map I’ve created. It’s in zipfile form, just unzip the file into the above folder and it’ll create the folder and included files and when you next start the game it’ll appear under “Custom Maps” in the battle browser.
Note that you now need to ‘edit’ then ‘save’ the map to recreate the bumpmap - this is because the bumpmap overlays are too big to include in a post on here, so I’ve removed it from the zipfile.
That map’s been difficult to balance. With the shared settings I can win an attack on ‘Captain’ difficulty but only just, and anything higher is nigh-on impossible. I keep trying to tweak starting and replenishment supply levels to balance, rather than changing the layout or deployment points, but I don’t want to leave the defence resource starved, and the map’s over too quickly for the attack to really take advantage of those multiple start points.
Comically exploring to find the files to post on here means I’ve found the config file that lets me override the map creator’s artificially low time limit (200000) which means I can now try doubling it and seeing if that helps the attack build up a sufficient supply of reserves to really push through the defence. I’ll have a go…
Cliffski, give us an in-game map sharing facility! 
File removed, due to newer version being included in post below
I quite strongly disagree with your assesment that this map is hard for an attacker to beat. I just beat the latest version you posted on the challenge board as attacker on the hardest difficulty. The problem for the defender comes from the attacker having SO many pathing options; i just force a ton of tanks down the upper route, then send fast mechs and supply trucks down the bottom route
Interesting. It may be that my defence/attack balance is skewed by the focus I’ve had so far in playing the game as a defender; I have a strong range of turrets I can deploy and I’m still trying to find a good attacking mix.
That in itself is going to make map balancing difficult. Different players will be stronger at attack or defence, so my contention that the map is biased towards the defender reflects my expertise in defence, yet is clearly at odds with your own experience. I think in a working multiplayer world you’d be able to upload your attack script and I could try and defend against it. Sadly at the moment I can’t seem to get that to work.
Thanks for the feedback though - the option of going north or south was deliberate (as is the bluff - head north then switch south) but I may have made the southern route too short to give defenders time to adjust to an attacking switch. An additional kink may help.
The merging of two paths into one that I have a couple of times on the north route is also causing traffic jams. With high damage units that’s good because it gives them time to break down the defence, but it makes the northern route hazardous for the more fragile attackers.
I’ll have a play with the layout, but I’m reluctant to do too many changes until we’ve had a proper match up of your attack vs my defence. I don’t doubt that you’ll prevail, but it’ll give me better direct feedback on where improvements are needed.
Hmm. Ok, boosted overall supply rates, with the defender getting a bigger boost than the attacker, and also made the southern route a little more elongated.
I still can’t win on Major difficulty in attack 
5744502116437288760811742155368Guernsey Assault v3.zip (102 KB)
Upload it to the challenge system, i’ll give it a whirl. And i’m pretty balanced between attack and defense; the trick is figuring out what works on BOTH attack and defense (hint: Yes, there is one build that works on both attack and defense, it’s why there’s one map i have yet to lose as defender on. Figure it out from my comments :P)
Battle 10060 - you’ve beaten it already, but I can’t see a response posted.
I’m still unlocking various modules, it could be there’s an offensive unit/combo I just haven’t had to deal with yet.
Hmm, ok. I’ve had a new unlock tonight, and it’s utterly swung the pendulum: Repair trucks on a map with multiple spawn points are just overwhelming.
2-4 repair trucks sharing each others’ repair field, stuck behind 2-3 slow high damage tanks, followed by 3-4 high damage mechs kind of sweeps the field before it. Nasty.
Now I understand why attack is dominating on that map
I generally don’t use Repair Trucks on that map, except for 1 spawned with my Supply Trucks. Honestly the resource rate means i can put on average 6 cheap units, or 4 heavy tanks, down at a time!