Hello Gordon,
Sorry to answer so lately, I just read your topic.
On my side, I remove the cover
and I insert a piece of wood ( part B ) in the hole
It is screwed with a base ( part A )
( I try to draw a picture because I am not at home
)
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Then tank is "upside down"
but I have not found another way to hold the tank
Actually, I keep the part A with second hand ( gloved hand ) in order to present all the "sides" for painting.
Good thing with PM tank is that upper surface is ( partially ) hidden by platform
And I use to paint with mat color
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I tried brilliant color for 2 tanks ( AGIP and Union Pacific ) but I agree it is not easy
( and I did not renouveller experiment .... )
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Do not forget to remove the cover and paint inside the hole
Sometimes I need to sand in the hole before painting.
If not, thickness of paint could prevent cover to return to its position