Can a sealed box be too big? Not technically, but it really depends on your goals. A bigger box is generally more efficient (less air 'spring' to push against) and will play lower. The tradeoff is flatter response (which can be less efficient at certain frequencies) and lower mechanical power handling. This power rating is called excursion limited power handling, and basically is the point at which the speaker can't move any further, and therefore, won't get any louder. So, if this number is lower, you can use less power (re: more efficient) to get full excursion, so its not really a tradeoff.

Once you get over 3 times the woofers Vas, you are technically infinte baffle (no box), and the box no longer has any effect on the woofer. I have built systems like this, and actually like the way they sound.

So to answer your specific question on Type R's. Alpine's site says 1.3 to 2.5 cu ft sealed each. Vas is 3.5 cu. ft. So, unless your box ends up more than about 18 cu ft (3xvasx2 woofers) it won't be infinite baffle, which isn't a bad thing anyway. You could always build a 5 cu ft box (alpine spec) and then use trim plates to fill in the space, if you want to be more precise.

Toby