enclosure for 2nt's

which is the best material, mdf or particleboard? mdf is the only one you have to seal the inside correct?

MDF is the best for sub enclosures. I rabbet and dado my enclosures so that they don't leak but I recommend using 100% RTV silicone to seal the joints no matter what material you use to build your box.

i am using liquid nails and 2" screws. which is the best sealant for the interior, i was thinking about using truck bed liner or can i line it with carpet?

NEVER use particle board, as it can literally fall apart, especially if used as a sub enclosure, and it absorbs moisture.  MDF is the best choice.  I assume you mean you want to cover the outside of the enclosure with carpet?  Don't "line" the inside!!

actually people said that you should seal the inside of a MDF enclosure to make it air tight.

Yes, the inside seams of any enclosure should be sealed.  Many people use RTV, which is very easy to work with.  Just be sure the RTV has completely cured (doesn't smell) before you mount your subs.  The inside surfaces of the enclosure do not need any treatment.  Be sure to read the enclosure building tips located on this site!

the tips says to line the inside. i am using liquid nails for the inside seams.

If you want to line the inside walls of an anclosure, do not use any sort of carpet.  Use acoustical foam, such as this product. There are other ways to dampen standing waves, but this stuff works the best that I have found.  Do not use it on the front baffle (where the drivers are mounted.)  I do not know about "liquid mails," but if it is a sealant that will create an air-tight bond between all your inside surfaces, go for it.  Don't forget to seal the area around the speaker wire terminals, the ports (if used) and around the driver itself (although I would think twice about using something permanent to mount the drivers, as this will prevent you from removing them.)

thanks for the info friend.