Just the bombs/DT's are permanent points...?
Yes, the bomb/drop-tank hard points on the P-38 series are on the airframe regardless of loadout.  Rockets are another story.
I thought the rocket rails on the 38's still came on/off and added drag.
Interestingly, the 5" rocket "rack" on the 38L, which does look rather lightweight and aerodynamic, 
 does not add any noticeable weight or drag after the rockets are fired.  The rocket tubes on the 38G and 38L do add weight and drag. 
 Here are my testing results and parameters for effects of rocket loadouts on the P-38 series:
All aircraft tested at 25% fuel, max ammo load, 5K no WEPP-38G IAS          Δ mph    Weight        Δ lbs          State
304 mph   -17        16,118     +1028 lbs    rockets on (6 x 4.5")
314 mph   - 7         15,290     +200 lbs      tubes only (rockets fired)
321 mph                15,090                        clean
P-38JIAS         Δ mph     Weight        Δ lbs          State
306 mph   -16        16,883     +1028 lbs    rockets on (6 x 4.5")
315 mph   - 7         16,055     +200 lbs      tubes only (rockets fired)
322 mph                15,855                        clean
P-38L  IAS          Δ mph    Weight        Δ lbs          State
306 mph   -16        17,255     +1400 lbs    rockets on (10 x 5")
322 mph     0         15,855     +0 lbs         racks only (rockets fired)
322 mph                15,855                       clean