Really, as long as you keep it in the realm of its advertised limits (2 in a pair = 30W RMS, 60W Max) and you don’t hear port noise, you’re ok. And when you think about it, you should be pushing somewhere near 100dB at 30W. That’s loud, and even more so in a Caravan. I think you’ll be alright.
And just to give you an idea of what you are looking for as a ballpark with (2) ND65 drivers on the faceplate in the same enclosure:
Inside Box Vol: 0.218 CuFt
Box & Port Freq.: 58.6 Hz
-3dB (F3): 46.5 Hz
1-1/2″ eqiv. round port: 5.3″ long
2″ eqiv. round port 9.8″ long
Sorry about the Imperial units, us Yanks are mostly still using them. 😁
You’ll have to play around with the port size in WinISD to make sure 1st resonance is not too low. I chose those sizes as standard ID pipes we can get here, because a pair of 2-1/2″ drivers is ~ equal to a single 3-1/2″ driver in piston area. Best part is, since you are going with a slot port, you can use whatever size (x-section area) you want, so you are not limited to what you can buy.