Definitely deep cycle. Also suggest you stick with conventional lead acid batteries, and stay away from gel and/or AGM. Not that they're bad, but conventional's likely better for you. Stay away from "no maintenance". You want to be able to maintain them by adding distilled water as needed.
A pair of Group 27's is fine, but may not be ideal, as you have no backup battery for starting. Another group 27 or group 24 starting battery, not deep cycle, would be nice insurance. Or, install a Victron battery monitor (search this site for much info). Knowing the percentage of charge you truly have left on your single bank would be nice.
A better setup still, would be a group 24 for starting backup, and all your house and regular starting needs provided for by a pair of 6v golf cart batteries wired for 12v (with a Victron monitor on them). I just did this setup on my Catalina 309.
But, I get that you're keeping it simple, so yes, the pair of deep cycle 27s will do the job without any changes required.
Interstates are OK.
As I upgraded my batteries, I found that the 40 buck membership fee at Sam's club more than paid for itself on my purchase of the batteries for my setup. Their batteries are branded as Duracells, and are actually made by Eastern Penn, which is a good maker.
