If making a watchtower from scratch is a little above your modeling skills, you might be interested in these very nice paper model watchtowers.
Paper Models
Paper Model Bait Ammo Beer and Grocery Shop
Here’s a nice paper model of a backcountry hillbilly or cajun grocery, bait, ammo and beer store.
Containers For Infinity and Other Science Fiction Games
You can get several designs of cargo containers for Infinity — or for any science fiction game, for that matter — at this Spanish site.
Free 3D Terrain For Dust Tactics
Top Solitario, one of my favorite sites for its quality free paper products, has a selection of 3-D terrain pieces for Dust and other games which can be downloaded, printed and quickly constructed — a bonus is that they also fold flat!