IF you are long underlying and Short Future on same
AT expiary they wil converge
But Is it not true that the cost of carry for the Long position is already factored in to the Futures price!
On One Chicago there is product caled "Exchange for Physical"
But the yiekd is hardly anything in USA
A) You own stock... ( LONG) + You sell Future on same at expiary you have to giv ethe stock
B) You have cash > You purchase stock > You sell Future on same
just be careful with how your broker finances your positions. if you're getting 'gross financing' then your the cash you get from long positions might not net off with the cash from your short positions. also, most brokers give you a spread such as: libor - 50 bps on your long cash, libor + 50 bps on your short cash. this can really eat the profit on basis trades.