Yes, Boracare can (and in many instances MUST) be used on pressure treated wood. As a termite barrier under Section VI of the label it is required to be applied twice to exterior wall sill plate and that is always pressuretreated.
All pressure treated wood that is cut or drilled MUST have a field treatment or end cut application in order to meet building code (including sill plate in a home - see IRC 2016 and AWPA Standard M4).
It is also useful to treat pressure treated wood as the heartwood is not treated properly by pressure treatment (especially refractory species such as Douglas fir, and the transition wood of pine decking is often the first to rot out and will greatly benefit from a treatment with Boracare with Moldcare at 5 years (see Lloyd et al., 2013).
Posts, piles and poles also have the heartwood issue and can be treated but this is often best done with Jecta.
Yes, it is fine to use any kind of insulation once the Boracare application is dry, typically in about 24-48 hours. Boracare will not interfere with an insulation application unless you do not allow the Boracare to be completely dry.
BORACARE should be applied, dried and ventilated prior to anyone returning to the treatment area. If treatment is just in the attic and you are not in the area during treatment, then you can stay in the home.
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.
If you have wood that you want to treat that is not already treated, painted, stained, etc., then you can apply paint, water sealant, or stain as long as a Boracare or Timbor treatment is dry. For Boracare you will usually need to wait at least 24 hours to make sure the application is completely dry. If you are treating wood that will be outside or otherwise exposed to rain and sunlight, then you should apply a water sealant to prevent the Boracare from breaking down over time.
Boracare contains borate, a form of Boron, that is different than boric acid products. Borate products are water soluble and are used in wood treatments as it can penetrate into the wood and/or used as a dust if using Timbor. Boric acid (dust) is not water soluble and is only for crack and crevice treatments. Both forms are not repellent but when dealing with subterranean termites Boracare is not the best product to use as it will only kills the termites that physically ingest the wood. This can cause the termites to start dying off quickly which sends a signal to the queen below ground that the area is bad and this can cause them to move to another location that is possibly untreated or inaccessible. It is a great product for Drywood Termites which are all in the wood they are infesting. When dealing with subterranean it is best to use a product like Termidor SC or Dominion which will be a slow kill and have a transfer effect so that it can kill the entire colony below ground.
Boracare can be mixed with hot water or used as a foaming agent. The amount of water will depend of the if you are doing a treatment for an active infestation or for preventative.
Foaming is the preferred method when treating voids. To foam a product you need a poly foamer to apply the foam and our ProFoam Foaming Concentrate which is an expanding liquid you need to mix with the solution. You would mix the Bora-Care with water in a one gallon poly foamer, then pour in the foaming agent, then mix it all together and pump up the poly foamer. You are now ready to foam voids.
As the beetles emerge from the wood after it has been treated with Boracare they will die from ingesting the treating wood so there would be no worry of reinfestation.