We have two gadgets that make a nice crisp base to a pizza.
One is a large non stick metal plate that has holes cut in it.The metal allows the pizza to cook,and the holes allow the heat to spread throughout the pizza bottom.These are available in most good supermarkets etc.
The other (for when we are having "posh" pizza) is a stone base,on which the pizza cooks.Being stone it again spreads the heat to the bottom of the pizza.This gadget also has a stand that the pizza (still on it's stone base) goes after cooking,and can be taken straight to the table.This has the hadded advantage that the stone stays hot,and keeps the pizza warm for quite a while(that is assuming you are not going to wolf it all down at once!)LOL
The stone gadget is available,but costs quite a lot more that the tin with holes,and is not so easily found in shops.
Bon Appetit molly.
PS:~
The problem with using tinned fruit is,no matter how much you may drain it the salt in the ham,and the cheese will draw out more(made worse by heat)
Of course you may be using too much tom puree(if this is from a jar) either way you really only need a very thin layer of tom.If you put too much filling on top it will never cook no matter how long or what temperature you use.