Hi ya, I have always used either Sanding Sealer specifically made for modelling by JP (J Perkins, London) or one made by Deluxe materials - that again is made for the modeller. I was lead to believe that the commercial sanding sealers e.g. the stuff that is used for woodworking and you buy from DIY contains a small amount of wax which can be a problem for us modellers - the other thing is I have also used when I have ran out of sand n sealer - Deluxe Eze Kote resin.
John
I have used both Shellac Sanding Sealer and Cellulose based Sanding sealer, both have worked without adverse reactions. The Shellac version is slower drying and a bit 'wetter', so can run about awkward shaped items, pooling before drying. The cellulose type is very quick drying. On a warm day and with a 36 inch boat, you can start at one end, work your way round the model, by the time you get back where you started, it will be dry and you can put another coat on.
I have also found that a pretty standard brush on all purpose primer from places like B&Q, will seal your grain and provide a pretty decent base coat. Even better if it can be rollered on. I have found it can be wet and dry sanded (lightly!) after about 45 minutes, to a very smooth finish.
Tried all three, would recommend all three, prefer the Cellulose option, just...