Boracare takes care of any active infestation of wood-destroying insects such as termites, carpenter ants, powderpost beetles, etc. It is possible for the wood to become infested again if it has been exposed to water, if the wood wasn't treated in any way, like if it wasn't stained, after the Boracare treatment dried or if not all exposed sides were treated.
Although, from the information you provided regarding the termite tunnels, if you're talking about mud tunnels then you are dealing with Subterranean termites. Boracare will still affect them if the eat the wood but the method of treatment to get rid of the colony will be to do a trench treatment around the Perimeter of your home with Termidor. Termidor can't be used indoors unless it's sprayed/foamed inside an enclosed wall void.
If you are sure, however, that you are dealing with Drywood termites, we recommend that you call Nisus (800) 264-0870 to troubleshoot with them as they are the makers of Boracare.
When using Boracare to treat for an active infestation of wood fungus it is applied at a 1:1 ratio for wood that is 4" thick or greater. Use a 3:1 dilution ratio for wood less than 4" in thickness. You can spot treat the areas that have active fungus and then use the 5:1 for future prevention in the non effected areas. You should be sure to address the moisture issue in the area before or during treatment of Boracare and apply a vapor barrier after the product has dried. Please see the product label for complete application instructions.
Foaming would definitely be the best option for your scenario. You mix Bora-Care as you normally would at a 1:1 ratio (one gallon of bora-care with one gallon of water). After you mix it, pour the solution in the foamer and add Pro-Foam foaming solution. You want a high expansion foam so you should mix 7 to 10 oz. of Pro-Foam per gallon of bora-care solution that you make. Then close the lid, shake the foamer, and pump it like you would any other hand pump sprayer. The Chapin Poly Foamer comes with a coiled hose and ¼ inch tapered nozzle. You can get the Chapin poly foamer in a 1 gallon model or a 2 gallon model.
Here are links for you to see:
Two gallon poly foamer: http://www.domyownpestcontrol.com/chapin-poly-foamer-gallon-2659-p-292.html
One gallon poly foamer: http://www.domyownpestcontrol.com/chapin-poly-foamer-gallon-2658-p-495.html
Profoam foaming agent: www.domyownpestcontrol.com/profoam-foaming-concentrate-p-307.html
Hope this helps. Please let me know if you have any further questions.