Please see photographs provided as best description, zoom is enabled.
I post all paper items protected and in proper card backed envelopes.
I'll always try and combine postage when I can.
I only use GSP for international postage, if non-UK and buying multiple items please do not pay until they have issued you with a final invoice as they cannot do so retrospectively.
I never add new folds, if I quote a parcel price it's because I can't fit it in a letter size envelope.
Thanks.