From my experience seal it with PVA as its much cheaper. Not done it yet but will. After sealing with PVA start to add an acrylic paint to the PVA to start a primer coat close to the end colour. Then do your plastidip coat, you wont need as much which will save you on plastidip that way. On my terminator build I lost lots of plastidip trying to get a think clean coat. So by adding paint to your PVA sealer coat you are making a flexible undercoat. Then theoretically you should only need one coat of plastidip if that makes sense. On my iron man foam helmet I will be doing 2-3 coats of PVA. Then on the bits that are chrome will add some black acrylic to the PVA to make a dark undercoat. Then will chrome it and then varnish for the final seal.