Different secondary design ?

Hi all,
Is it possible to create a secondary without a pipe on the inside I asked
If so, there would be no loss from the PVC I now use.
The idea was to use a PVC pipe and grease it slightely, or use mylar or
something else
to put between the PVC and copper windings to be removed later, wind the copper
aroud it, coat it, and of course let it get hard, gentely pull the PVC out and
clean the
wire from whatever youv'e put between it and coat it several times for
strenghtening the
wire from collapsing on it's own
Or maybe if done with mylar inbetween, leave the mylar as your secondary form.
So, is this something that has potential, or has someone allready done this ?
I reallise this can only be done with rather small TC's, `cause a big coil
would fall in on it's
own weight.
greetings from Jeroen Kooiman from a really HOT and sunny (30C) Holland