Here is what you need to do open your data ini file for the F-105 scroll down the weapon stations and find-->
[LeftWingStation]
SystemType=WEAPON_STATION
StationID=3
StationGroupID=2
StationType=EXTERNAL
AttachmentPosition=-3.27,-2.42,-0.23
AttachmentAngles=0.0,-5.0,0.0
LoadLimit=1600
AllowedWeaponClass=BOMB,ARM,EP,MER,RP,FT,CGR
AttachmentType=USAF
ModelNodeName=pylon_left_middle
PylonMass=108.41
PylonDragArea=0.06
FuelTankName=Tank450_F105 <--- Change to ( f105_450gal_sea )
RackLimitOutsideOnly=TRUE
Change the RightWingStation just like above. For the center line station find the 650 gal SEA tank using the weapon editor and copy the name in the top left box marked Type and paste it just like you did with the two above.
You will always have these tanks even if you choose the silver paint. I think you may be able to get around that by using the Loadout ini. I will take a look at that and let you know but for know you have your SEA tanks.