Flow resistance of EVAP canister too high.
Purge air line blocked.
Evap canistor purge valve open.
There are tests a shop with a PST2 can perform to narrow the possible causes down.
I would need to find my Boxster OBD2 reference to post any details of the tests. (I misplaced this book!)
P1128 and P1130 can be caused by several things, but the significant cause I think in this case is "EVAP canister purge valve open".
Thus I would suspect the purge valve. I hate to advise you to throw parts at the symptom but in this case replacing the valve might be a reasonable shot in the dark. I of course offer no guarantee a new valve is going to solve your problems.
But if the part is not that much and the effort is not too great...
If you replace the valve, of course check all hoses/lines for any breaks, cracks, signs of damage/age/distress. Clear teh error codes and then drive the car a while. Probably 30 miles or so is long enough to see if the codes (any codes) reappear.
Sincerely,
MarcW.