Plan around the trough rather than the peak. Build a forecast that runs a full trading cycle so you can see how deep the quiet period goes and how long it lasts, then work out how much cash you need to carry through it. Seasonal businesses fail on the gap, not on the busy months.
Practical levers include deposits or staged payments on advance bookings, tighter stock ordering so cash is not tied up out of season, and negotiating supplier terms that reflect your trading pattern. Some businesses find off-season products or services that partially offset the dip, though that only helps if it does not divert cash from the core trade.
On the funding side, options can include facilities structured around your season, refinancing assets you already own to release working capital, or spreading tax bills over the year instead of paying in lump sums that land in a quiet month. Each of these adds cost and a repayment obligation, so the saving in cash flow terms has to be worth it.
Be honest in your forecast about how bad a poor season could be. Funding arranged on optimistic assumptions leaves you committed to repayments in a year that does not go to plan.