Think you should be able to cooperate and construct TW defenses during the TB between TWs. But once TW's start up, you can no longer build any more. Then you have to figure out how to use what you've made over the week over two consecutive TW's. (or maybe not - and just keep building it up for another week)
Each person can get resources just from their normal daily activities and battles - then they need to make up shield generators, auto-turrets, med-pac's, shock grenade, walls (bonus % to dodge?), mines (1-2% damage to enemy at start of fight), whatever. You can add them to other peoples teams once deployed.
It'd kind of keep TW going all the time and as some of better content we've gotten recently, it could be pretty fun. Give's a some incentive to a scrappy guild that's really active.