Jon: It's really going to depend on the wing design. For two data points, here is how my two a/c were done.
Stinson L-5B: The tank is a drop in unit. The front and rear sides have lips that rest on the spars. The wing has numerous ribs that are cut so that the bottom of the tanks rests on felt cushions. The tanks are secured by straps over the top of the tank, secured to the front and rear spars, pulling them tight against the bottom of the wing. All exposed edges of the tanks are then taped and doped as the wing is covered.
Fairchild AT-21: the tanks are bottom loaded into the wing with straps under the tanks drawing them tight against the upper structure. The stiffeners above the tanks have profiles cut into them corresponding the the upper tank form and are covered with felt or rubber strips to prevent fretting. The lower skin in the area of the tank access is a stress panel and is screwed to the front and rear spars. There are a number of formed ribs on the stress panel that have rubber strips on them and contact the bottom of the tanks to help keep them tight to the structure and minimize movement.
Whatever route you take, remember that unless your tank is going to be a structural element, you will need to account for the absence of full strength ribs in the tank area. You could place multiple tanks between ribs, but that not only complicates fuel flow, returns, venting and filling of the tanks, but also adds considerable weight for the installation.
Food for thought...