Hank … knew in advance that the door has bullet holes covered with duct tape.
I vaguely remember thinking:
Looks like a bullet pattern from when a gun was fired from immediately outside or inside the door - probably inside given the height of the pieces of tape.
Hank could plainly see that the tape was there. Given the pattern of pieces of tape and his suspicions of what the RV had been used for (making extremely valuable illicit drugs), a 'pattern of bullet holes' would be near the top of his mind.
As to why Hank did not answer - he knew they 'had him', in the sense that he did not have Probable Cause to suspect a crime (as opposed to suspicions and hunches) and therefore no authority to remove the pieces of tape.
It would have been tainted evidence that the court would not accept, and more importantly, would have resulted in all evidence from the RV to be dismissed..
The reason cops do things like Hank did when he removed the tape, is that they are hoping to trick or panic the suspect into making a confession or revealing something that can be used as evidence. Then they 'fail to make a record' of the illegal part of what they did .. & hope that it does not come up in court. Alternately they might fib and claim that the tape was already partially peeled off when they saw the hole.
In Hank's case, he had the (very legally savvy, and not shy) junk yard owner who had witnessed him removing the tape. I think it was already established by then that the owner was not only clever, but also unafraid of challenging police officers. After he was challenged by Jessie as well, Hank realized he would not get away with the usual tricks.