Im guessing the low IBU count is from the low isomerization of the alpha acids in the hops due to the pretty thin wort until the last 15min. That said, 33 still seems crazy low for a 70min boil of any hops. I would do a small charge around 45min of a 45min boil then use the rest of the hops in the last 15-0 minutes of the boil. EDIT: Oh, wow, only a 10L boil? Yeah, 30g is way way too much for that long.
Far as the Carapils sub. Gladfield Gladiator Malt seems to be the equivalent. Carapils just adds dextrin and supposed to help with foam stability. If foam stability is all you want, Id go for a bit of flaked wheat or flaked barley, unless you want the touch of added sweetness.