I have used a carpeted ramp in the past and it worked ok but when I purchased my H30 I was sitting in the salon designing the ramp and my large dog got impatient and just ran down the ladder. I didn't think it was possible as the ladder was quite steep. Since then we always have a rubber backed runner on the ladder and he prefers a spotter at the bottom for going up or down.
Before you build the ramp try carpet and some treats for incentive with a hand on his chest to steady him on the way down. My dog is getting pretty old now as the H30 was traded for a C350 and then a C42 but he still does the trip up and down with a bit of help from the spotter. We also have rubber backed rugs on the sole of the salon and in the cockpit for good traction.
You mentioned that you lifted him in and out, that must have been difficult. You might try training him by lifting and letting him help out with an "assisted climb" until he gets the hang of it.
If that does not work and you need to go with a ramp, I recommend Solvit brand ramps. They have strong lightweight designs with a non-skid surface that is corrogated for extra traction. I use that for getting from the dock to the boat.
http://www.solvitproducts.com/
Here is a shot of one of their more challenging boarding situations. The solvit ramp is the run from the stairs to the swim ladder.