Number one tip is remove the backing before you apply. The directions usually say to apply with the backing on. Do not do this unless you want creases and bubbles.
I use rapid tac instead of soapy water, for me it works a bit better.
I usually eyeball the alignment but sometimes a piece of tape here or there might be needed as a landmark.
Make sure the tank and decal is nice and wet before you place the decal. It will "float" a bit but not much. Hold on both ends and touch down on the center first and sorta roll it down on both ends. If you didn't land it correctly pick it up and try again but first spray some more. Once down start in the middle and very gently rub with your finger mostly lengthwise to establish your position. If still looks good keep rubbing with finger to smooth it down slowly working your way lengthwise and gradually working height wise as well. Make sure you are pushing any creases or bubbles out towards the edges. Keep edges wet at all times! If a crease or bubble is beginning to become trapped or is too big to work out, gently pull up the edge and try that area again working out bubbles or creases with your finger. Light finger pressure only. You may need to carefully use a razor blade to lift edge. Keep spraying to keep edges and any areas not down yet wet. Eventually you should have it all down with no creases or bubbles. It's tricky. You have to be patient. Once it looks good, you can squeegee from the center out. Once you start using the squeegee you cant undo it.
I'm thinking an RD400 shouldn't be too bad. The ones with compound curves are the hard ones!
As for when to add decals, I do it after several coats of clear, sand, add decals, then more clear.
I use rapid tac instead of soapy water, for me it works a bit better.
I usually eyeball the alignment but sometimes a piece of tape here or there might be needed as a landmark.
Make sure the tank and decal is nice and wet before you place the decal. It will "float" a bit but not much. Hold on both ends and touch down on the center first and sorta roll it down on both ends. If you didn't land it correctly pick it up and try again but first spray some more. Once down start in the middle and very gently rub with your finger mostly lengthwise to establish your position. If still looks good keep rubbing with finger to smooth it down slowly working your way lengthwise and gradually working height wise as well. Make sure you are pushing any creases or bubbles out towards the edges. Keep edges wet at all times! If a crease or bubble is beginning to become trapped or is too big to work out, gently pull up the edge and try that area again working out bubbles or creases with your finger. Light finger pressure only. You may need to carefully use a razor blade to lift edge. Keep spraying to keep edges and any areas not down yet wet. Eventually you should have it all down with no creases or bubbles. It's tricky. You have to be patient. Once it looks good, you can squeegee from the center out. Once you start using the squeegee you cant undo it.
I'm thinking an RD400 shouldn't be too bad. The ones with compound curves are the hard ones!
As for when to add decals, I do it after several coats of clear, sand, add decals, then more clear.