Forecast a full trading cycle so you can see the size and length of your quiet period, then decide before the season starts how you will fund it. Preparation done in the peak, when cash is available and lenders see strong trading, is far easier than arranging finance in the trough when the numbers look weakest.
Practical measures include setting aside a proportion of peak-season cash rather than spending it, provisioning for VAT and corporation tax as you go, timing large purchases for months when cash allows, and negotiating supplier terms that follow your pattern rather than working against it.
Review your cost base too. Fixed costs that continue year-round are what make a seasonal trough painful, so anything you can make variable — subcontracted rather than employed capacity, for example — reduces the depth of the dip.
Where funding is part of the plan, options can include facilities with a seasonal repayment profile, refinancing assets you already own to release working capital, or spreading tax bills. Each adds cost and a commitment you will need to meet in a bad season as well as a good one, so arrange it against conservative assumptions.